A recent paper published in the journal Nature, reports the results of sequencing the genomes of all fourteen of the so-called Darwin’s finches, found on the Galápagos islands (1). These, now famous bird species evolved from a common ancestor as recently as 1.5 million years ago (possibly 2.3 mya) according to previous mitochondrial DNA dating, adapting to different habitats and forming separate species on the basis of beak size and shape, body size, plumage and feeding habits.
I must confess that I found them all very confusing when I visited the Galápagos islands, and in truth never succeeding in confidently identifying them. I was never quite sure if I was looking at a small, a medium or a large ground finch! So it comes as no surprise to me to find out from this latest work, that genes have been flowing back and forth between the species, which have been hybridizing to form new species of mixed ancestry throughout this period! What is new, is the discovery that a gene (called ALX1) which is responsible – although they may be other factors involved – for determining beak shapes. These birds have been changing and evolving beak sizes and shapes in response to environmental change, and this is still going on (2). Changes in the genomic DNA (i.e. mutations) associated with such a gene produce the phenotypic variation – in beak size and shape – that can be selected in response to environmental changes such as droughts, which regularly occur on these islands (2).
This present study builds on the phenomenal work carried out by Peter and Rosemary Grant (of Princeton University) who have been studying Darwin’s finches since 1973. They had previously found that in some situations, on some islands, there is so much interbreeding that two separate “species” might fusing back into one species (3). In other words, although the species have diversified (a process called adaptive radiation) there are in effect, no great barriers between them, to prevent the exchange of genes. To my mind, it all points to a great plasticity within nature. What we see now, is in effect a snap-shot in time (our time, the Anthropocene) but changes which produced the extant species will carry on – assuming we allow these iconic species enough space and protection to continue evolving into the future.
As a footnote, I should add that all of the ground finches shown here were photographed at the airport on Baltra Island. They seemed to be adapting very successfully to Man’s presence, even flying into the restaurant and stealing food. Not sure if anyone is studying these individuals! I’ll call them Medium Ground finches, but I’m not sure!
1. Sangeet Lamichhaney, Jonas Berglund, Markus Sällman Almén, Khurram Maqbool, Manfred Grabherr, Alvaro Martinez-Barrio, Marta Promerová, Carl-Johan Rubin, Chao Wang, Neda Zamani, B. Rosemary Grant, Peter R. Grant, Matthew T. Webster, Leif Andersson. Evolution of Darwin’s finches and their beaks revealed by genome sequencing. Nature, 2015; DOI: 10.1038/nature14181
2. Grant, Peter R., and B. Rosemary Grant. How and why species multiply: the radiation of Darwin’s finches. Princeton University Press, 2011.